Oscillation generator



I .-f lower bias.

Patented May 31, 1938 PATENT oFFicE OSCILLATION GENERATOR Jan Schalkwijk, The Hague, Netherlands, assignor to Telefunken Gesellschaft f-iir Drahtlose Telegraphic m. b. H., Berlin,-G'ermany, a corporation of Germany Application July 27, 1935, Serial No. 33,472 In Germany July20, 1934 2 claims. (01. 179-471) This invention relates to oscillators and more particularly tocircuits employing multigrid electron discharge tubes for producing high frequency oscillations.

It is well known that oscillator tubes may be so constructedas to exhibit a so-called dynatroneffect, that is to say an effect which may be attributable to secondary emission. If, for example, the grid of a triode is made more positive than the anode, and if the anode consists of a material capable of secondary emission, then secondary electrons will be supplied by the anode when primary electrons impinge thereon. The

number of secondary electrons quite frequently exceeds that of the'primary electrons. The secondary electrons pass to the grid electrode since the latter has the higher potential and, there.- fore, theyfiy toward the. primary electrons. In this manner an anode current characteristic appears which reveals a descending slope oi" its curve such as may be utilized for the setting up of oscillations.

The dynatron effect which may be observed in a triode, as above described, gives rise to the term anode'dynatron as applied to such a triode since it is the anode that furnishes the secondaryelectrons. There is also what is known as a grid dynatron in which the anode hasa positive bias and the grid likewise a positive, but If it is assumed that a sufficiently high potential is impressed upon the grid. with respect to the cathode and the grid is of a material capable of secondary emission the grid supplies secondary electrons which are absorbed by the plate and the grid current characteristic reveals a .portion of its curve with a descending slope.

Both the anode dynatron and the grid dynatron can be usedv for setting up oscillations, if

in the circuit of'the electrode capable ofsecondaryemission a resonance condition is provided. For this purpose one generally employs a tank. circuit consisting of parallel disposed capacitive inductive elements and tuned to the 1: frequency to be produced.

The dynatron? arrangement has the advan tage over the ordinary feed-back circuit in that it issimple in structure and does not produce skipand-disruption phenomena, and furthermore an oscillatorso constructed is .comparatively free from harmonics and parasitic oscillations. One drawback which has not heretofore been satisfactorily overcome in the use of the dynatron arrangement relates toa certain instabilityof the secondary emission effect, but it is among the objects of this invention to overcome such a disadvantage by providing a multigrid tube, the structure of which will be hereinafter described in more detail.

My invention finds particular utility in transmitter circuits, and also in a self-oscillating mixer stage in connection with superheterodyne receivers.

According to the invention the electrode ca pable of secondary emission isenclosed between two electrodes maintained at a higher potential, these electrodes being suitably formed as screen grids. The utilization circuit is preferably connected with still another electrode.

The features of my invention which are consideredto'be' novel have been set forth in the appended claims. The details of construction, however, as well as the mode of operation will be described in the following portion of the specification and may be best understood upon reference to the accompanying drawing in which Figure 1 shows diagrammatically one embodiment of an oscillator circuit employing a multigrid tube;

Fig. 2 shows a'somewhat different embodimentwhich also employs a multigrid tube; and

Fig. 3 illustrates a fragmentary portion of the diagram of Fig. 1 modified so as to' provide for speech modulation.

Referring to Fig. l which elements of a transmittercircuit, it may be seen that I have provided means particularlysuited to the generation of low power oscillations where-' in the frequency is maintained constant within remarkably close tolerances; I

The energy for operating this circuit may be derived from a transformer T having a primary l connected to any suitable source of alternating current. The secondary winding 2 feeds energy through a rectifier '4 and thence to a filter circuit comprising the two capacitors 5 and 6 which are connected across opposite terminals respec tively of the resistors l and 8. The directcurrent potential so obtained may then be impressed upon the cathode l8 and the double grid l8 of the oscillator tube l4, thus providing a suitable positive potential upon the double grid IS with respect to the cathode. The cathode I 6 may be heated in the usual manner by a filament I5 which derives its heating current from the secondary winding 3 on the transformer T.

If desired, for the purpose of impressing a greater load upon the tube I 4, chokes may be substituted in place of. the resistors 1 and 8.. A closed circuit for the filter is provided by the represents certain v quency.

voltage divider consisting of resistors 9 and H]. An intermediate voltage may be derived from a tap connected between the resistors 9 and i and led through a tank circuit comprising the inductance l3 in parallel with which is a capacitor l2, and thence it may be impressed upon the grid l9. This grid 19 is enclosed by the two grids I 8 and emits secondary electrons. Suitable operating voltages are obtained if, for example,

the grid I9 is maintained at between '70 and 80 volts while the grids [8 are maintained at around 150 volts.

The aforementioned capacitor 12 in parallel with the inductance l3 constitutes a frequency determining circuit in connection with the grid l9.

Connected with the cathode I6 is a grid I! which is positioned immediately surrounding the cathode and within the other grids. If desired, the grid I! may be made slightly more positive than the potential of the cathode or it may even be made more negative.

The oscillations set up in the tube l4 may be utilized by taking them off from the plate circuit which includes the anode 20, the primary winding 22 of a transformer, a resistor 24 and a return circuit to the cathode by way of a switch 25 having contacts a and b for alternative connection with different portions of the aforementioned filter. Y

The utilization circuit itself is shown connected with the secondary winding 23 which is inductively related to the primary winding 22, there being interposed therebetween a suitable electrostatic shield 2l which is grounded so as to eliminate the possibility of feed-back from the work circuit into the oscillator tube of undesirable capacity effects.

It has been found to be of particularly great advantage that the work circuit is connected to an electrode different from the electrodes of the oscillatory circuit per se, since it provides complete freedom of the oscillator circuit from work circuit reaction. The independence of the oscillator circuit from the work circuit is furtherinsured by making the grids [8 of screen formation.

The circuit arrangement of Fig. 1 lends itself to a variety of different modulating systems. When the switch 25 is in contact with the segment a, then the anode 20 will be supplied with filtered direct current and the oscillations will be unmodulated. If, however, the switch 25 is thrown into contact with the segment b, then the anode will receive unfiltered direct current and the os cillations will be modulated with the line fre- In a receiver, particularly one which employs push-pull ormultiphase detection, the second and higher harmonics of the fundamental frequency will be obtained. If another modulating frequency as, for example, speech is to be transmitted from the microphone 4| and amplifier 42, then a transformer 43 'may be inserted in the anode circuit by means of which a modulating voltage may be superposed on the steady potential applied to the anode 20, in which case 1 the switch 25 is obviously to be placed in contact with the segment a.

A further very interesting modification of my invention may be had if the oscillator circuit is adapted to produce secondary emission from the anode 20. In this case the direct current potential applied to the anode should be considerably lower than that applied to the grids Hi. It will be found then that the plate current characteristic has a descending slope. Now, if in the plate circuit, an oscillatory circuit'tuned to the modulation frequency is inserted, then this circuit will be excited in its natural oscillation and the high frequency oscillations will be modulated due to the dynatron effect of the grid l9.

Referring now to Fig. 2, the adaptation of my invention to a self-oscillating mixer stage will now be described.

Only such portions of the receiving circuit as are necessary to an understanding of the invention have been shown in the circuit diagram of Fig. 2. They comprise an antenna A feeding energy to the primary winding 25 of a transformer T, and thence through its secondary winding 27 to an input circuit for the tube 43, this input circuit being connected between the cathode l and the control grid 39, The input circuit may be tuned by inserting a tuning condenser 28 in parallel with the secondary winding 27. A suitable negative bias may be impressed upon the control grid 30 by means of the bias battery 29. Between the control grid 30 and the anode are located a double walled screen grid 3| which surrounds, both interiorly and exteriorly, a grid 32. Suitable operating potentials may be impressed upon the various electrodes of the tube 40 as shown by.

the terminals V+, V'+ and V"+ respectively in relation to the potential of the cathode I6 which is V-.

In the circuit of the grid 32 there is placed a frequency determining tank circuit comprising the inductance 33 and the capacitor 34. It is in this circuit that the dynatron characteristic appears. The resonance circuit 33-44 is tuned to the superheterodyne frequency. The oscillations of the energy collected on the antenna are then combined with the oscillations, the frequency of which is determined by the tank cir cuit 3334, and either a sum frequency or a difference frequency may be derived in the output circuit which includes the anode 2B and a tank circuit comprising the capacitor 35 and inductance 36. This tank circuit may be tuned to the desired intermediate frequency. Furthermore, the inductive winding 36 may be coupled to a secondary winding 31 through which the output energy may be taken off and utilized, say, in an intermediate frequency amplifier 38 feeding to any desired utilization device.

Due to the arrangement shown in Fig. 2 in which successively higher voltages are impressed upon the grids 3i and the anode 20 in respect to the grid 32, it may be seen that secondary emission takes place from the grid 32. There is, however, a very decided advantage to be had from the arrangement of the several grids 30, 3! and 32 as shown, in that the mixing of the oscillations to be heterodyned is greatly facilitated.

I claim:

1. In an oscillation generator, an electron discharge tube having a cathode, an anode, and a multiplicity of grid electrodes of screen-like formation, one of said grid electrodes being adjacent the cathode, the second and fourth grid electrodes being conductively interconnected, and a third grid electrode being positioned intermediate the second and fourth grid electrodes, a resonant circuit connected to said third grid electrode, an output circuit connected to said anode, means including polarized circuits between said cathode, said grid electrodes and said anode for so applying direct current potentials to said electron discharge tube that oscillations are caused to be set up therein and secondary emission is derived from said third grid electrode, and means for superposing upon said output circuit energy of a is impressed upon the first mentioned grid electrode relative to the potential of the cathode, means for enabling the grid electrode of lower positive potential to emit secondary electrons,

an output circuit connected betwen the anode 5 and cathode, means for modulating said output circuit, and means for retaining said cathode, anode and grids in suitable spaced relations to one another whereby the modulating effects are prevented from reacting upon said oscillatory 10 circuit.

JAN SCI-IALKWIJ K. 

